Method and arrangement to detect an oil leakage between sections of a hydraulic cylinder

ABSTRACT

Provided is an arrangement and a method to detect an oil leakage between a first section and a second section of a hydraulic cylinder. A movable piston is arranged between the first and second section in a way that the piston changes position between the sections. The change in position is done in dependency of a difference between a first force, which acts at the first section on a first cross sectional area of the piston, and a second force, which acts at the second section on a second cross sectional area of the piston. The first section comprises hydraulic oil with a predefined first pressure, while the first force is calculated based on this pressure and based on the first area. The second section comprises hydraulic oil with a predefined second pressure, while the second force is calculated based on this pressure and based on the second area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application No.PCT/EP2017/080462, having a filing date of Nov. 27, 2017, which is basedon German Application No. 10 2017 203 049.6, having a filing date ofFeb. 24, 2017, the entire contents both of which are hereby incorporatedby reference.

FIELD OF TECHNOLOGY

The following refers to an arrangement and to a method to detect an oilleakage between a first section of a hydraulic cylinder and a secondsection of the hydraulic cylinder. The hydraulic cylinder is used in ahydraulic pitch drive system of a wind turbine.

BACKGROUND

Modern wind turbines are showing a number of three rotor blades, whichare rotating around a horizontal axis of rotation. The rotor blades areconnected with an electrical generator to convert wind energy intoelectrical energy.

Each rotor blade can be aligned into the incoming wind by typically twohydraulic cylinders, being part of a hydraulic pitch drive system.

Hydraulic oil is applied by pressure to each hydraulic cylinder. Thehydraulic cylinder comprises a first section and a second section, whilea movable piston is arranged between the first section and the secondsection.

Hydraulic oil is applied to these sections, creating forces, which areacting on the respective area of the piston. In example: A first forceF1 is created at the first section according to this formula: F1=P1*A1while P1 is the pressure at the first section and while A1 is therespective cross-sectional area of the movable piston, which is exposedto the pressure P1.

A second force F2 is created at the second section according to thisformula: F2=P2*A2 while P2 is the pressure at the second section andwhile A2 is the respective cross-sectional area of the movable piston,which is exposed to pressure P2.

Based on the difference of the forces F1 and F2 the movable pistonchanges its relative position—it might be moved towards the secondsection for example if the situation is like this:F1>F2P1*A1>P2*A2

With A2=A1−Arod and with Arod as those cross-sectional area of a rodbeing part of the movable piston and reducing the respective area A2 theformula results in:P1*A1>P2*A1−P2*Arod.

Thus, the movable piston will be pushed towards the second section ifP1≥P2.

Based on the respective formulaF1<F2P1*A1<P2*A1−P2*Arodthe movable piston might be pushed towards the first section by choosingrespective values for P1 and P2, taking into account the knowncross-sectional areas A1 and Arod.

The hydraulic cylinder always comprises a high-pressure section and alow-pressure section and a respective high-pressure side andlow-pressure side.

The movable piston interacts via its position change and via a root endbearing with the blade. The root end bearing is a functional part of theblade and is used to set a specific pitch angle of the blade.

In detail the rod of the movable piston is coupled with or is acting onthe root end bearing.

A service report revealed that most hydraulic cylinders will failbetween operation year seven and operation year eleven according to aWeibull distribution. The failure results from a leakage of hydraulicoil.

Hydraulic oil might leak externally, leaving the hydraulic cylinder andthe hydraulic system itself.

Hydraulic oil even might leak inside the hydraulic cylinder, which isknown as internal leakage: i.e. if there is a leakage at the movablepiston hydraulic oil might be transferred between the first and thesecond section in an uncontrolled manner.

The internal leakage often evolves over time and results in an increasedpumping and circulation of oil in the hydraulic system, which mightcomprise the cylinder, an oil-reservoir, oil supply connections, a pump,valves, etc.

An internal leakage cannot be detected easily as the hydraulic oil staysinside the hydraulic system and cannot be detected by checking the levelof the hydraulic oil in the oil-reservoir for example.

The hydraulic system tries to compensate external oil losses by usingoil, which is stored in the oil reservoir. Thus, a loss of hydraulic oilcan be detected easily by service personal, checking the oil leveltherein.

The effects of oil leakages will increase over time and will finallyresult in an operational error, which is reported to a control of thewind turbine. Depending on the rank of the report signal an alarm,calling for service, might be signaled to a control center.

Each wind turbine is checked and serviced in given time periods, i.e.there might be an annual inspection. Thus, service personal might detectan external oil leakage visually as described above or the servicepersonal might notice an (internal) oil leakage by given report signals.

Especially for offshore wind turbines, showing a guaranteed lifetime of25 years or more, maintenance work for hydraulic components is a hugeand costly problem.

It was found that such wind turbines might require in a worst-casescenario two hydraulic cylinder exchanges over the lifetime of the windturbine. Due to the harsh offshore environment service time isrestricted and limited while equipment, which is needed for the servicework, might be expensive as well.

SUMMARY

An aspect relates to an improved method and arrangement to detect aleakage of a hydraulic cylinder reducing or avoiding the problems givenabove.

According to embodiments of the invention an oil leakage between a firstsection of a hydraulic cylinder and a second section of the hydrauliccylinder is detected. A movable piston is arranged between the firstsection and the second section in a way that the piston changes itsposition between the sections. The change of the position is done independency of a difference between a first force, which acts at thefirst section on a first cross sectional area of the movable piston, anda second force, which acts at the second section on a second crosssectional area of the movable piston. The first section compriseshydraulic oil with a predefined first pressure, while the first force iscalculated based on this pressure and based on the first area. Thesecond section comprises hydraulic oil with a predefined secondpressure, while the second force is calculated based on this pressureand based on the second area. The first section is connected with aremote controlled first valve. This first valve is closed for theleakage detection. A sensor is coupled with the movable piston in a waythat any change in its position is detected. The change of the positionresults from the difference of forces, which is in return resulting fromthe closed valve and from the alignment of the first pressure to thesecond pressure due to the leakage, which is between the first sectionand the second section. The sensor is coupled with a control, which isprepared and arranged to detect the leakage of oil based on the changeof the position.

In a preferred configuration the piston interacts via its position witha blade of a wind turbine thus the blade is turned via the piston andother components to specific pitch angles.

In a preferred configuration the pitch angel is chosen between 0° and15° for detecting a leakage of oil as these blade angles are mostrelevant for wear and tear of the blade.

The 0° pitch angle represents a position of the blade, wherein the bladesurface, facing the wind, is essentially turned in the rotor plane asseen from a chord-wise direction. Accordingly, a 90° pitch angle refersto the “feathered position” of the rotor blade, wherein the bladesurface is turned out of the wind.

In a preferred configuration the controller-software will test thecylinder for internal leakage several times a year. The aligned rotorblade pitch drive will be parked at a given testing time in one of thesepositions: 0°-10°-15° as described above.

In a preferred configuration the hydraulic cylinder is part of ahydraulic pitch drive system of a wind turbine.

In a preferred configuration the control is the controller (the centralcontrol unit) of the wind turbine, providing the control signals andinitiating and performing the oil leakage detection automatically and ina remote-controlled manner.

Thus, all relevant surveillance signals of the whole wind turbine arecombined at the wind turbine controller.

By performing this controller-based leakage detection any internalcylinder defects are detected quite early. Thus, faulty cylinders can bereturned to the supplier for reimbursement as long as the respectivewarranty period has not lapsed.

A wind turbine often starts to report errors according to this sequence:

-   -   Report: pumping time becomes prolonged,    -   Report: temperature of the hydraulic oil starts to increase, and        finally an    -   Report: an unwanted pitch tracking occurs during the wind        turbine operation.

In a preferred configuration this sequence is additionally taken intoaccount to initiate the leakage control or leakage detection. Thus, theleakage in the cylinder is detected quite early and before severedamages of the cylinder took place.

In a preferred configuration the controller-software will test thecylinder for internal leakage some times a year. The aligned rotor bladepitch drive will be parked at a given testing time in one of thesepositions: 0°-10°-15° as described above.

The embodiments allow a self-diagnostic procedure of the hydraulicsystem (hydraulic cylinder), which is done remote controlled.

The embodiments can be implemented with a cheap software package,programming the cylinder self-test on the wind turbine controller,taking into account limits of the piston movement.

Thus, all other relevant components are controlled easily by softwareand without the need for additional hardware and without implementationwork for hardware.

Due to embodiments of the invention operational stops, which areimplemented in prior art wind turbines for security reasons, andunnecessary maintenance visits can be avoided. This results inconsiderable cost savings especially for offshore wind turbines.

Thus, the wind turbines can be triggered to perform an oil leakage teston demand to avoid severe damages just in time.

If a production series of cylinders is known to be burdened withtroubles the respective cylinders can be checked more often than usual,leading to an increased system security.

Unplanned cylinder exchanges can be avoided by an optimized and adjustedmaintenance service interval.

Additionally, a more constant functionality and lubrication is achievedby embodiments of the invention, thus the overall lifetime of thecylinder is prolonged as well.

The cylinder wear depends on the site of the wind turbine thusturbulences might affect the lifetime negatively. Taking this intoaccount as well embodiments of the invention allows a certain predictionof an exchange of a cylinder.

BRIEF DESCRIPTION

Some of the embodiments will be described in detail, with references tothe following Figures, wherein like designations denote like members,wherein:

FIG. 1 shows a schematic view of an arrangement in accordance withembodiments of the present invention; and

FIG. 2 shows a schematic view of a wind turbine, which is equipped withthe oil leakage detection in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION

FIG. 1 shows the arrangement.

A hydraulic cylinder HC comprises a first section S1, while hydraulicoil HO is provided in and out of the first section S1 by a predefinedfirst pressure P1.

The hydraulic cylinder HC even comprises a second section S2, whilehydraulic oil HO is provided in and out of the second section S2 by apredefined second pressure P2.

The hydraulic cylinder HC comprises a movable piston MP, which isarranged between the first section S1 and the second section S2 in a waythat the movable piston MP changes its position POS between the sectionsS1 and S2.

The hydraulic oil HO is applied to these sections S1 and S2 thusrespective forces F1 and F2 are created.

A first force F1 is created at the first section S1 according to thisformula:F1=P1*A1.

P1 is the first pressure at the first section S1, which acts on a firstcross sectional area A1 of the movable piston MP.

A second force F2 is created at the second section S2 according to thisformula:F2=P2*A2.

P2 is the second pressure at the second section S2, which acts on asecond cross sectional area A2 of the movable piston MP.

For this example, the effective cross-sectional areas A1 and A2 showthis dependency:A2=A1−ARODwhile AROD is the cross-sectional area of a rod ROD, being part of themovable piston MP.

The first section S1 is connected with a first valve V1, which is openedor closed remote controlled by a first control signal CS1.

The second section S2 is connected with a second valve V2, which isopened or closed remote controlled by a second control signal CS2.

A sensor SEN is coupled with the movable piston MP in a way that anychange in the position POS of the movable piston MP is detected. TheSensor SEN is coupled with a control unit CONT, which is prepared andarranged to detect a leakage of hydraulic oil HO based on the change ofthe position POS.

Let's assume a leakage LKG between the first section S1 and the secondsection S2 exists, i.e. due to a faulty seal of the movable piston MP.

For the cylinder leakage test the first valve V1 is closed remotecontrolled by the controller CONT.

Thus, in case of a hydraulic cylinder HC without faults the pressure P1should be somehow “frozen” in its value.

Due to the leakage LKG the first pressure and the second pressure willadapt to each other thus finally the first pressure P1 will show thesame value than the second pressure P2:P1=P2

For the respective forces this situation results in:F1=P1*A1F1=P2*A1and forF2=P2*A2F2=P2*(A1−AROD).

By comparison of the forces F1 and F2 it is shown that for a leaking LKGin the hydraulic cylinder HC:F1>F2as the second (active) area A2 is smaller in its value than the first(active) area A1.

Thus, the movable piston MP will change its position into the directionof the second section S2.

Summoned up if there is a leakage LKG in the cylinder HC the pressuresP1 and P2 will be equate and due to the known active areas A1 and A2 themovable piston MP will change its position POS.

The change of the position POS will be detected by the sensor SEN,resulting in the knowledge that the hydraulic cylinder HC shows aninternal leakage LKG.

FIG. 2 shows details of a wind turbine WT, which is equipped with theoil leakage detection according to embodiments of the invention.

The movable pistons MP (as described in FIG. 1 ) of i.e. two hydrauliccylinders HC1, HC2 interact with the blade BL thus the blade BL isturned into specific pitch angles PA.

For the leakage detection the pitch angel PA is chosen between 0° and15°, thus the surface of the rotor blade BL is aligned and turned in anoptimum manner into the incoming wind W.

These blade pitch angles are most relevant for wear and tear of theblade.

The hydraulic cylinders HC1, HC2 are part of a hydraulic pitch drivesystem HPS of the wind turbine WT.

The wind turbine control CONT is used to provide the control signalsCS1, CS2 and to perform the oil leakage detection automatically.

Although the invention has been illustrated and described in greaterdetail with reference to the preferred exemplary embodiment, theinvention is not limited to the examples disclosed, and furthervariations can be inferred by a person skilled in the art, withoutdeparting from the scope of protection of the invention.

For the sake of clarity, it is to be understood that the use of “a” or“an” throughout this application does not exclude a plurality, and“comprising” does not exclude other steps or elements.

The invention claimed is:
 1. A method comprising: receiving an errorreport sequence from a wind turbine, the error report sequenceincluding: (i) a pumping time becoming prolonged, (ii) a temperature ofthe hydraulic oil starting to increase, and (iii) an unwanted pitchtracking occurring during operation of the wind turbine; and initiatinga detection of an oil leakage between a first section of a hydrauliccylinder and a second section of the hydraulic cylinder in response tothe receiving the error report sequence, wherein an arrangement of thewind turbine is used to detect the oil leakage, the arrangementcomprising: a movable piston arranged between the first section and thesecond section in a way that the movable piston changes a positionbetween the first section and the second section dependent on adifference between a first force, which acts at the first section on afirst cross sectional area of the movable piston, and a second force,which acts at the second section on a second cross sectional area of themovable piston; wherein the first section comprises hydraulic oil with apredefined first pressure, while the first force is calculated based onthe predefined first pressure and based on the first cross-sectionalarea, and the second section comprises hydraulic oil with a predefinedsecond pressure, while the second force is calculated based on thepredefined second pressure and based on the second cross-sectional area;wherein the first section is connected with a remote controlled firstvalve, which is closed for the leakage detection; wherein a sensor iscoupled with the movable piston in a way that any change in position isdetected, while a change of the position results from the difference ofthe first force and the second force resulting from closing the remotecontrolled first valve and from an alignment of the first pressure tothe second pressure due to the leakage between the first section of thehydraulic cylinder the second section of the hydraulic cylinder; whereinthe sensor is coupled with a control unit, which is prepared andarranged to detect the leakage of oil based on the change of theposition.
 2. The method according to claim 1, wherein the sensor coupledwith the movable piston is located remote from the hydraulic cylinder.3. A wind turbine comprising: a plurality of rotor blades; a hydraulicpitch drive system for aligning a rotor blade of the plurality of rotorblades into incoming wind; and an arrangement for detecting an oilleakage between a first section and a second section of a hydrauliccylinder of the hydraulic pitch drive system, the arrangementcomprising: a movable piston of the hydraulic cylinder that interacts,via a position of the movable piston, with the rotor blade to turn therotor blade to specific pitch angles, wherein the movable piston isarranged between the first section and the second section in a way thatthe movable piston changes the position between the first section andthe second section dependent on a difference between a first force,which acts at the first section on a first cross sectional area of themovable piston, and a second force, which acts at the second section ona second cross sectional area of the movable piston; wherein the firstsection comprises hydraulic oil with a predefined first pressure, whilethe first force is calculated based on the predefined first pressure andbased on the first cross-sectional area, and the second sectioncomprises hydraulic oil with a predefined second pressure, while thesecond force is calculated based on the predefined second pressure andbased on the second cross-sectional area; wherein the first section isconnected with a remote controlled first valve, which is closed for theleakage detection; wherein a sensor is coupled with the movable pistonin a way that any change in position is detected, while a change of theposition results from the difference of the first force and the secondforce resulting from closing the remote controlled first valve and froman alignment of the first pressure to the second pressure due to theleakage between the first section of the hydraulic cylinder the secondsection of the hydraulic cylinder; wherein the sensor is coupled with acontrol unit, which is prepared and arranged to detect the leakage ofoil based on the change of the position; wherein detecting the oilleakage is initiated in response to the wind turbine reporting asequence of errors including: (i) a pumping time becomes prolonged, (ii)a temperature of the hydraulic oil starts to increase, and (iii) anunwanted pitch tracking occurs during operation of the wind turbine. 4.The wind turbine according to claim 3, wherein the remote controlledfirst valve is connected with the control via a first control signal,thus hydraulic oil is provided in and out of the first section in aremote controlled manner.
 5. The wind turbine according to claim 3,wherein a remote controlled second valve is connected with the controlvia a second control signal, thus hydraulic oil is provided in and outof the second section in a remote controlled manner.
 6. The wind turbineaccording to claim 3, wherein the pitch angle is chosen between values,which are most relevant for wear and tear of the blade, the pitch anglebeing between 0° and 15° for detecting a leakage of oil.
 7. The windturbine according to claim 3, wherein the control unit is the controlunit of the wind turbine, providing the control signals and performingthe oil leakage detection automatically in response to the reporting ofthe sequence.